<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>红路灯倒计时</title>
    <style>
        .box {
            width: 250px;
            height: 52px;
            padding: 15px 30px;
            border: 2px solid #ccc;
            border-radius: 16px;
            margin: 0 auto;
        }

        .box .count {
            width: 60px;
            color: #666;
            font-size: 280%;
            line-height: 50px;
            padding-left: 6px;
            margin-left: 5px;
            border: 1px solid #fff
        }

        .box div {
            margin-left: 5px;
            float: left;
            width: 50px;
            height: 50px;
            border-radius: 50px;
            border: 1px solid #666;
        }

        .gray {
            background-color: #eee;
        }

        .red {
            background-color: red;
        }

        .yellow {
            background-color: yellow;
        }

        .green {
            background-color: #26ff00;
        }
    </style>
</head>
<body>
<div class="box">
    <div id="red"></div><!--红灯-->
    <div id="yellow"></div><!--黄灯-->
    <div id="green"></div><!--绿灯-->
    <div id="count" class="count"></div><!--倒计时-->
</div>
</body>
<script type="text/javascript">
    /**
     * @Description:
     * @author 朱志文
     * @date 2021/10/27
     */
    var lamp = {
        red: {
            obj: document.getElementById('red'),
            timeout: 30,
            style: ['red', 'gray', 'gray'],
            next: 'green'
        },
        yellow: {
            obj: document.getElementById('yellow'),
            timeout: 5,
            style: ['gray', 'yellow', 'gray'],
            next: 'red'
        },
        green: {
            obj: document.getElementById('green'),
            timeout: 35,
            style: ['gray', 'gray', 'green'],
            next: 'yellow'
        },
        changStyle(style) {
            this.red.obj.className = style[0];
            this.yellow.obj.className = style[1];
            this.green.obj.className = style[2];
        }
    };
    var count = {
        obj: document.getElementById('count'),
        change: function (num) {
            this.obj.innerHTML = (num < 10) ? ('0' + num) : num;
        }
    };
    var now = lamp.green;
    var timeout = now.timeout;
    lamp.changStyle(now.style);
    count.change(timeout);

    setInterval(function () {
        if (--timeout <= 0) {
            now = lamp[now.next];
            timeout = now.timeout;
            lamp.changStyle(now.style)
        }
        count.change(timeout);
    }, 1000)
</script>
</html>